The invention relates to a system and method for controlling fuel vapor purging in a vehicle equipped with an internal combustion engine coupled to a fuel tank coupled to a purging canister.
Vehicles typically have various devices installed for preventing and controlling emissions. One of the sources of emissions are fuel vapors generated in the fuel tank due to temperature cycling and fuel vapors that are displaced in the process of refueling the fuel tank. In order to remove these vapors from the fuel tank, vehicles are equipped with fuel emission control systems, typically including a fuel vapor storage device, which in this example is an activated charcoal filled canister for absorbing the evaporative emissions. One such system is described in U.S. Pat. No. 5,048,492, where a three-way connection between the fuel tank, the canister and the engine is established. The engine is connected to the fuel tank and the carbon canister via a communication passage. Vapors generated in the fuel tank are continuously drawn into the canister where the fuel component (usually hydrocarbons) is absorbed on the carbon granules, and the air is expelled into the atmosphere. A purge control valve is located in the intake manifold of the engine between the engine and the canister. A controller selectively opens and closes the purge control valve to allow purged fuel vapors from the canister to enter the engine. When the valve opens, manifold vacuum from the engine draws air from the atmosphere back into the canister, thus purging the fuel vapors into the engine, where they are burned.
The inventors herein have recognized a disadvantage with the above approaches. Namely, since vapors are always being generated in the fuel tank, and therefore are always exiting the tank due to the fact that it is not isolated, it is not possible to detect fuel tank conditions that may lead to fuel vapor emission into the atmosphere such as a missing or improperly installed fuel cap.
An object of the present invention is to develop better diagnostic procedures of the fuel vapor purging system.
The above object is achieved and disadvantages of prior approaches overcome by a method for detecting a fuel tank condition in a vehicle, the method consisting of: isolating the fuel tank from a fuel vapor storage device and from an engine; calculating an estimated rate of change of a fuel tank pressure based on an operating condition when the fuel tank is isolated; calculating an actual rate of change of said fuel tank pressure when the fuel tank is isolated based on an information from a fuel tank pressure sensor; and indicating the fuel tank condition if said actual rate of change exceeds said estimated rate of change by a value greater than a preselected constant.
An advantage of the above aspect of the invention is that the proposed system configuration allows isolating the fuel tank for diagnostic purposes. By isolating the fuel tank, system diagnostics will be able to tell whether the fuel vapor emission into the atmosphere is occurring due to a fuel tank condition or is caused by some other component of the fuel vapor purge system. This e will decrease the time required to diagnose and repair the fuel vapor purge system, and will therefore improve service time and cost.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.